In image sensors such as CMOS image sensors, cross-talk may be generated between pixels. Specifically, optical cross-talk is generated if light enters a neighboring pixel adjacent to a target pixel by being transmitted through a dielectric layer between metal lines. In such an instance, a photodiode obtains improper information, and thus, outputs an incorrect image. In particular, cross-talk mixes data together to cause color mixing. In case of photographing a bright image, creation of a bright background thereby results.
Example FIG. 1 illustrates a cross-sectional diagram of an image sensor in which light is transmitted through a microlens and enters a neighboring pixel instead of a target pixel. A lower structure of such an image sensor may include shallow trench isolation (STI) film 104, a plurality of photodiodes and transistors provided at predetermined locations in pixel and peripheral areas on and/or over semiconductor substrate 102.
As illustrated in example FIG. 1, an image sensor may include first photodiode 106, second photodiode 108 and gate electrode 110 of a transistor. By way of example, example FIG. 1 shows a pair of photodiodes and a single gate electrode 110 indicating a transistor, and other photodiodes and transistors are omitted in order to simplify the illustration of example FIG. 1. Boro-phosphor-silicate glass layer (BPSG) 112 serving as a pre-metal dielectric (PMD) layer and first capping layer 114 are formed on and/or over the lower structure of the image sensor. BPSG layer 112 and first capping layer 114 are then patterned, contact 116 for an upper line structure is formed, and first metal line 118 is then formed on and/or over capping layer 114. Subsequently, first interlayer dielectric (ILD) layer 120 and second capping layer 122 are stacked on and/or over first metal line 118 and first capping layer 114.
Second metal line 124 is formed on and/or over second capping layer 122 and second ILD layer 126 and third capping layer 128 are then stacked on and/or over second metal line 124 and second capping layer 122. Subsequently, second ILD layer 126 and third capping layer 128 are patterned to form via 129 and third metal line 130 is then formed on and/or over third capping layer 128. Third metal line 130 is electrically connected to second metal line 124 by way of via 129 despite that third metal line 130 and second metal line 124 exist on different layers, respectively. After forming undoped silicate glass (USG) layer 132 on and/or over third capping layer 128 and third metal line 130, nitride layer 134 is stacked thereon. Subsequently, color filter layer 136, planarization layer 138 and microlens array 140 are sequentially formed on and/or over nitride layer 134. Hence, an image sensor having a three metal structure is completed.
As illustrated in example FIG. 1, optical paths A, B and C are explained as follows. Each optical path B and C indicates that light transmitted through microlens array 140 enters a corresponding diode. However, optical path A indicates that light passing through insulator between metal lines enters first photodiode 106 adjacent to second photodiode 108 that is a target diode. Consequently, optical cross-talk is generated. Light passing through microlens array 140 may enter an unexpected photodiode by being reflected and/or refracted on various metal wires and/or interlayer layers, thereby causing cross-talk.